Brian Patrick, an entomologist with Wildland Consultants and co-author
(with his son) of the book "Butterflies of the South Pacific (2012)", responded.

In New Zealand we do indeed have both white and black butterflies. But the
white butterfly species are much more likely to be encountered as the black
butterfly species are specialists living in of our highest mountains of the
South Island. Whereas the white butterflies are lowland species living in
settled areas and in the case of the cabbage white being at times extremely
common from backyards to farmed areas.

As their common name suggest white butterflies are mostly white in colour,
with varying numbers of black spots and mustard-coloured undersides to the
hindwings. Both our species belong to the butterfly family Pieridae, a large
worldwide group of reasonably similar-looking species. Both the cabbage
white (1930) and large white (2010) are accidentally introduced species as New
Zealand has no indigenous members of this large family.

While the cabbage white marched un-checked through the country throughout
the 1930s from its entry point at Napier's port, a reasonably successful eradication
programme appears to have almost eliminated the large white in the Nelson
region where it probably came in through the Port of Nelson. Both species as
caterpillars are pest of plants in the cabbage family with the large white also
laying its eggs on nasturtium leaves.

On the other hand black butterflies are almost completely black or very dark
brown in colour with varying numbers and positions of small white spots.
Recent studies by my son Hamish and I has revealed a rich fauna of these
gorgeous butterflies in the alpine and high-alpine areas of New Zealand's
South Island, where they frequent scree and fellfield. This habitat of
mainly rock is a harsh environment for a butterfly, being covered in snow
for many months over the winter period and then in summer awash with
sunlight with nowhere to hide on the hottest summer days. The caterpillars
of these butterflies feed on small grasses that grow sparsely on these
slopes. Up until recent years it was thought that we had just one species of
these butterflies, but my son as a twelve-year old questioned this
hypothesis, and then set about a study that culminated in his Honours Thesis
at Lincoln University in 2012 where he used the latest genetic techniques to
clearly show we had many more species, all with their own distinct
distribution and appearance. In fact he found up to three species on some
alpine areas where they emerge at different times over the summer, but with
periods of overlap.

We now have evidence for 11 species with many places having
two or three species flying together, but remaining distinct. We have never
found a hybrid specimen. These are glorious inhabitants of our highest
mountains and can be locally common there. They are a marvellous reward for
anyone who ventures into our most remote wilderness areas over the summer
months.